Root Cause Analysis: On the Rails

Root Cause Analysis: On the Rails

When Iarnród Éireann Irish Rail (the national railway operator of Ireland), started seeing an increasing number of failures of bearings in a particular fleet of rolling stock, it wanted to track down the cause – but soon faced a complex situation requiring an external viewpoint.

“We were experiencing problems with bearings on relatively new stock,” said Damien Lambert, technical support manager – bogies and wheel sets. The previous three years had presented an increase in premature breakdowns in journal bearings. “We started to explore the issue with the supplier and manufacturer, but it soon became evident that an independent external view was required to get to the root cause of the problem.” Romax Technology provided a solution.

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(Photos courtesy of CIE Group)

In this case, the axle box bearing provides support for the vehicle weight and dynamic loads during service such as curving. Iarnród Éireann Irish Rail had observed a wobbly wheel phenomenon: actually a wobbly axle box. The bearings (double row taper bearings, typical for this type of intercity train) were expected to provide a service life of three million kilometers but some were failing at only 750,000 km. Lambert described this as “the highest failure rate on any bearing in this fleet. Not catastrophic failures, but the condition of the bearings at overhaul were such that an unacceptable percentage could not be overhauled. It’s a relatively new fleet so there are cost implications.”

“We didn’t have preconceived ideas on causes, or the types of analysis needed,” Lambert said. The various parties debated whether it was a bearings issue, loading issue or another cause. “We knew we needed some degree of modeling and analysis of loads. Romax’s submission covered that. We chose Romax because of the expertise it demonstrated. Value for money was also important.”

Romax pitched three work packages, which included using RomaxDesigner software as “a faster, more effective and streamlined way to achieve the company’s goals. “We could do what we needed but at a controlled cost and with faster processing times. We didn’t enter into this contract lightly: we knew these issues were being disputed and findings would be queried, so reports had to stand up – they would be pulled apart. Another reason was the experience Romax demonstrated on similar investigations. We knew it was more than capable of delivering what we wanted,” Lambert said.

Lambert added that it was important not to prejudge possible outcomes. The initial scope and remit was deliberately broad, enabling Romax to start broad and so examine all possible causes, with the work packages. The output was three reports, showing a process to eliminate non-contributing root causes with recommendations and suggestions for further investigation.

“Sensitivity analysis was particularly beneficial, and showed that no single issue was likely to have caused the degradation. So while no definitive root cause was established, we could rule out certain issues, with results suggesting multiple causes,” Lambert said. This included water ingress initiated by a static condition and unequal loading as a contributory factor.

The company also looked into  further grease sampling, determining the effects of static loads caused by bogie to wheel set tolerances, general suitability of the bearings, improved sealing and the suspension set-up for additional research.

(www.romaxtech.com)

Editor’s Note: Be sure to check out the August issue of PTE for a detailed look at some of the key developments in bearing software from Romax, Schaeffler, KISSsoft, Timken and SKF.

Categories: Editors Choice

About Author

Matthew Jaster

Matthew Jaster, Senior Editor, has a B.A. in journalism from Columbia College Chicago and has 15+ years of writing and editing experience in automotive, manufacturing, engineering, law and arts and entertainment.

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